Look like you are new in construct so I will explain you step by step what to do and show you all the animation property's
1.Double Click on the Sprite you wanna edit
2.In the animations Windows click the animation you wanna change or edit values(when you create a new sprite it came with a fixed name of Default which you can change as you like).
3.Look at the property by default is at the left of the screen if you cant see the property-> Go to View and click on the Property Checkbox.
in there you will see some value that you can freely edit as you want.
Speed -> this is the speed of the animation which is determinate frame per seconds Ex. if you set it to one then every 1 second it will change to the next frame of the animation if it set to 2 it will display two frames per second.
Loop-> if it set to yes it will repeat the animation on finished if it set to no it will go through all the frame and stay in the last this depend too in the Speed to make it work if the speed is set to 0 frame persecond this will likely stay at the first frame.
Repeat Count is used if to loop a animation in a certain times like if you set it to 2 then it will loop two time and then it will stay in the first frame.
Repeat to -> if you want the animation start from frame let say 1 instead of 0 then it will loop starting from the number you put in there.
Ping pong -> is used to reverse the animation.
*to fix your problem
set Speed to something bigger than 0
and set loop to yes
I hope this help ya